New Catto prop - stack crush plates?

prkaye · #1 10-24-2014, 02:55 PM

I just received my new Catto prop (with nickel edges). This is to replace my Catto prop I got about 4 years ago. The new prop is thinner, and they supplied a retrofit crush-plate to make up the difference. I plan to go out to the hangar this weekend to do the prop swap. My question for any other Catto customers who have done this - will I be stacking the two crush plates (my old one and the new one), or just replacing the old one with the new one?
I'm asking here because I think Catto has closed for the day (for the week), and I'd like to install the new prop this weekend.
Thanks!

alpinelakespilot2000 · #2 10-24-2014, 05:52 PM

Phil,
I replaced a thick steel crushplate with 2 aluminum crush plates from Saber in order to take some of the weight off my nose. Saber recommended stacking the two aluminum plates together (equalling the thickness of the original steel crushplate) so that I could use my existing (expensive) prop bolts. So, according to Saber, I guess the answer to your question would be yes. Hope this helps.

Dbro172 · #3 10-24-2014, 05:53 PM

What about different length bolts instead? Does the spinner need to be changed out too?

alpinelakespilot2000 · #4 10-24-2014, 05:58 PM

Derek has a good point. You will probably need to put the Catto-supplied crush plate aft of the forward spinner bulkhead so that your spinner still fits. Your original crush plate would then go forward of the fwd spinner bulkhead. Either way, your existing bolts should work so long as the combined thickness of the new prop + catto supplied crushplate = the thickness of your original prop.

prkaye · #5 10-24-2014, 06:00 PM

The thicker crush plate (5/8") was supplied by Catto with the new prop precisely so that I could use my existing prop bolts and spinner. This is what they do for customers like me who are replacing one of the older (thicker) 3-blade props with the new thinner prop. The thicker crush plate is supposed to compensate for the thinner hub of the newer props.
According to my old and new invoices, the old prop thickness was 4.375 and the new prop is 3.75. This is a difference of exactly .625 = 5/8. So, by the arithmetic, I will need to use both crush plates to get the equivalent overall setup I now have.

Quote:

You will probably need to put the Catto-supplied crush plate aft of the forward spinner bulkhead so that your spinner still fits. Your original crush plate would then go forward of the fwd spinner bulkhead.

This sounds right to me. Maybe there's some instructions or notes hidden in the prop box... I only peeked inside today - I'll look for notes when I unpack it tomorrow.
Maybe this has been a silly question - I guess I only hesitated because, for an assembly that is so critical and that is spinning around at such high RPMs, it seems to me that one would want to avoid stacking-up any more discrete parts than necessary.

RV3bpilot · #6 10-24-2014, 11:04 PM

You may need the extra crush plate thickness to hold the front spinner bulkhead in the right place.

RV-4 · #7 10-25-2014, 01:24 PM

Phil

I did the same as you ( Replacing a Catto 3 bladded with a new Carbon fiber 3 blades ) and had to buy a new spinner because I sold the old one with the prop.

Once I received the crush plate from Saber ( Craig forgot to put it in the box ) I couldn't installed the spinner with the new crush plate, had to use the old thinner crush plate and the spinner fitted like a glove.

I never use a second crush plate in front of the forward bulkhead, is it a requirement??

Mine is a 12'' spinner installed on an RV-4..

Bruno
rv4@videotron.ca

prkaye · #8 10-27-2014, 06:22 AM

So it was as was speculated by others. It was pretty obvious once I got the spinner off and looked at things. The 5/8" crush plate goes behind the forward spinner bulkhead. This compensates for the fact that the new prop hub is 5/8" thinner than the old prop hub, and brings the spinner bulkhead properly into position. Then the old crush plate goes on the front of the forward spinner bulkhead, just like before.

The installation was actually pretty seamless - took less than an hour. Looks nice and flies just like my old prop.

Quote:

I never use a second crush plate in front of the forward bulkhead, is it a requirement??

Good question - I wondered this myself. So you just put the washers under the prop bolts right up against the spinner bulkhead? The only thing I wonder about is putting that much localized stress directly against the thin bulkhead material (those bolts are torqued to 38 ft lbs). The forward crush plate distributes that stress evenly throughout the whole spinner bulkhead. Also, the new prop is lighter, so the extra crush plate keeps my C of G roughly where it was before.

Question - with composite props I know (from experience) that the prop bolts have to be re-torqued after some initial amount of time... I guess the composite layup gets compressed a bit and sort of settles-in. How many hours of operation, or how many days/weeks of time should I wait before pulling that spinner, cutting the lockwire, and re-torquing those bolts. Do you think I'm safe to go 5-10 hours, say a month?

rv7charlie · #9 10-27-2014, 07:57 AM

For a new wood prop, I like to recheck after 1st flight, then after maybe 3-5 hrs. After that, the next time the cowl's off/annual.

I do it after 1st flight to verify that everything 'seated' correctly on installation, and that there's no defects that were hidden during installation.

In 20+ years of flying wood props, I've never seen torque change after the 5 hr mark, and I live in the deep south, where humidity varies from sometimes 20% or less in winter to swimming levels in summer.

FWIW,

Charlie

roadrunner20 · #10 12-26-2014, 06:15 PM

Quote:

Originally Posted by alpinelakespilot2000

Phil,
I replaced a thick steel crushplate with 2 aluminum crush plates from Saber in order to take some of the weight off my nose. Saber recommended stacking the two aluminum plates together (equalling the thickness of the original steel crushplate) so that I could use my existing (expensive) prop bolts. So, according to Saber, I guess the answer to your question would be yes. Hope this helps.

Any idea of the weight differerance between the aluminum vs steel crushplate of the same thickness?

Just curious as I really need to add some weight on the nose to offset the aft cg. I've been flying 8 years & when I converted from the A model to Taildragger, my cg went further aft.